The Service Employees International Union has long boasted that it is on the cutting edge of the labor movement. But the union found itself badly embarrassed this week when it was named in the federal criminal complaint charging Democratic Gov. Rod Blagojevich of Illinois with maneuvering to secure financial gain from the appointment of the state's next U.S. senator.

The complaint said Blagojevich's chief of staff, John Harris, had suggested to a service employees official that the union should help make the governor the president of Change to Win, a federation of seven unions that broke away from the AFL-CIO. The complaint said Blagojevich was seeking a position that paid $250,000 to $300,000 a year.

In exchange, the complaint suggested, Blagojevich had expected the service employees union and Change to Win to seek to persuade him to name President-elect Barack Obama's first choice, Valerie Jarrett, to succeed Obama in the Senate. The union would also receive help from the Obama administration, presumably for its legislative agenda.

Several union officials in Chicago and Washington said the service employees official approached by Harris was Tom Balanoff, the president of the union's janitors local in Chicago and head of the union's Illinois state council.

Balanoff, one of the union officials closest to Obama, is widely seen as an aggressive, successful labor leader, who has helped unionize thousands of janitors not just in the Chicago area but also in Texas.

The Illinois branch of the service employees issued a statement Wednesday night saying, "We have no reason to believe that SEIU or any SEIU official was involved in any misconduct." It added that the union and Balanoff were cooperating with federal investigators.

Change to Win's spokesman, Greg Denier, said the federation "had no involvement, no discussion, no contact" with Blagojevich or his staff about Obama's successor. "The idea of a position at Change to Win was totally an invention of the governor," Denier said, "and his stance has no basis in reality."

Denier added that the presidency of Change to Win was an unsalaried position. The federation's president, Anna Burger, is the service employees' secretary-treasurer and receives only her union salary.

Service employees officials said the criminal complaint did not accuse the unnamed "SEIU official" of having done anything wrong. All the official did, they said, was listen to Blagojevich and his chief of staff and ferry some messages for them.

A senior SEIU official who insisted on anonymity because prosecutors had asked union officials not to talk said his union was one of many that backed Blagojevich and received favors from him.

But he said it was understandable that Blagojevich would ask the service employees for a favor because it was so powerful and was one of the unions closest to Obama. (Patrick Gaspard, the former political director of the SEIU's huge New York health care affiliate, 1199, was political director of Obama's campaign and has been named the White House political director.)

If Blagojevich was going to approach a union to help land a high-paying job after leaving the Illinois governorship, it probably made sense for him to approach the service employees, the nation's fastest-growing union.

With more than 1.8 million members nationwide, it is the largest union in Illinois, was an early and generous backer of his ambitions to become governor, and received some important favors from him.

In 2005, the governor issued an executive order that enabled the service employees to unionize 49,000 in-home child care providers who were paid through state and federal funds. Afterward, the service employees negotiated a 39-month contract that raised the child care providers' daily rates by 35 percent on average and provided them with health coverage.

With Blagojevich evidently hoping to trade favors with Obama, the service employees seemed like a sensible intermediary because it was widely seen as having done more than any other union to elect Obama. The service employees' political action committee spent at least $26 million on Obama's behalf in the presidential campaign, making it by far the largest single PAC donor in the campaign.

The service employees union was also the top overall donor to Blagojevich's 2006 re-election campaign, with records showing it donated more than $900,000, or about 5 percent of his total campaign funds.